I have a few old bricks RCX and I have bought a new NXT which has more possibilities. But I need more than 3 motors and so, I'd like to make communicate NXT with RCX. A solution is to use "mechanical" communication with a motor on NXT and a rotation sensor on RCX. The position of the axe is a "message" for the other brick.
But i've seen that there was a IR modul for NXT sold by HITechnic. Is there a way to use this modul with RobotC?
Maybe someone has another idea to make them communicate?

Thanks and congratulations for RobotC , it's a fantastic tool for NXT programmation

RCX as slave is a good idea -- however, once you plan to purchase an expansion, you may want to check the motor multiplexer from mindsensors.

Both Hitechnic and Mindsensors sell Ir modules that let you communicate back and forth between a RCX and NXT. Both of them will allow you to send motor commands to the RCX, like MotorA forward, backward, off, Run Program 1-5, beep, shutoff RCX. The will also let you command the IR lego train, or the new power functions motors.

Both of these sensors can be programed with RobotC, Mindsensors has basic RobotC code on their website to use the RCX as a slave with their NR-Link. I havent seen anyone release RobotC code for the Hitechnic one yet.

Good luck with your project B-)
Scott